1. Field of the Invention
This invention relates to a disposable syringe, more particularly to a disposable syringe which enables a needle cannula to be retracted within a plunger cavity having a reduced pressure therein.
2. Description of the Related Art
Referring to FIGS. 1 and 2, U.S. Pat. No. 5,176,640 discloses a hypodermic injection syringe 10 which includes a barrel 11, a base 12 fixed to an open front end 111 of the barrel 11, a needle cannula 13 having a rear needle end 132 that extends into the barrel 11 through the base 12 along an axis and that has an engagement recess 131, and a plunger 18 slidable within the barrel 11. The plunger 18 includes a hollow shaft 14 with a vacuum chamber 141, and a head which has an elastic rubber ring 16 with a channel that is closed by a disc 161, and a plug 15 with a tube forcibly inserted into the channel of the ring 16 and secured to the shaft 14. A piston 17 is slidable in a sealed manner within the chamber 141, and is provided with an engaging rod 172 formed with an elastic flap 171 on a front end thereof.
In use, when the plunger 18 is about to finish its injection stroke, the disc 161 is lacerated by the rear needle end 132, the rod 172 then engages the needle 13 by engagement of the flap 171 and the engagement recess 131. In this state, under the action of vacuum present in the chamber 141, the rod 172 and the needle 13 are sucked into the chamber 141.
Since the needle 13 can be retained in the chamber 141 of the plunger 18 for safety disposal, the following drawbacks arise:
1. The laceration of the disc 161 may occur when the injection procedure of the syringe 10 is not finished. Thus, some medicine or blood may will remain within the barrel 11 to result in contamination.
2. In order to smoothly suck the needle 13 into the chamber 141, the securing of the needle 13 to the base 12 cannot be very tight. However, insufficient securing of the needle 13 will result in movement or removal of the needle 13 during the injection procedure.
The object of the present invention is to provide a disposable syringe which can prevent trapping of medicine or blood therein after injection and which can be operated easily and smoothly to retract a used needle within a plunger.
According to this invention, the disposable syringe includes a needle cannula, a barrel, a tubular barrier member, a tubular needle seat, and a plunger. The barrel has an inner surrounding barrel wall surface surrounding an axis and confining a passage with opposite rearward and forward openings. The inner surrounding barrel wall surface includes a larger-diameter segment and a smaller-diameter segment which confine rear and front passageways, respectively, to form a surrounding shoulder portion therebetween. The smaller-diameter segment includes a smaller front surrounding region and a larger rear surrounding region to form a surrounding abutment wall therebetween. The larger-diameter segment includes proximate and distal surrounding regions respectively proximate to and distal from the surrounding shoulder portion. The proximate surrounding region has a retaining area spaced apart from the surrounding shoulder portion.
The tubular barrier member includes front and rear surrounding edge portions, and inner and outer barrier wall surfaces. The outer barrier wall surface is retained at the retaining area by virtue of a first frictional force generated therebetween while in water-tight engagement with the proximate surrounding region, thereby partitioning the rear passageway into a compressible chamber confronting the surrounding shoulder portion, and an accommodation chamber confronting the rear surrounding edge portion. The inner barrier wall surface has a grip segment.
The tubular needle seat includes a hub portion disposed to fix the needle cannula therein. The hub portion has a surrounding front end wall, a surrounding gripped portion and an anchoring portion. The surrounding gripped portion is retained at the grip segment by virtue of a second frictional force generated therebetween when the surrounding front end wall abuts against the surrounding abutment wall and when the needle cannula is disposed outwardly of the forward opening.
The plunger is movable in the accommodation chamber, and includes a plunger body and a seal member. The plunger body includes a top end wall disposed movably to abut against the rear surrounding edge portion of the tubular barrier member, and a bottom end wall extending outwardly of the rearward opening so as to be manually operable. The top end wall has an inner peripheral edge portion surrounding the axis to define a cavity therein. The cavity extends along the axis and towards the bottom end wall to contain a fluid at a reduced pressure. The seal member is disposed to be sealingly attached to the inner peripheral edge portion along a sealing line so as to trap the fluid in the cavity.